1. Field of the Invention
This invention relates to clusters and more particularly relates to selecting a cluster.
2. Description of the Related Art
A storage system may include a plurality of tape drives that are used to access a plurality of magnetic tapes using a library manager. The magnetic tapes may be disposed within cartridges. A controller may direct an actuator to move a tape cartridge from a storage area to tape drive in order to access data written on the magnetic tape and/or to write data to the magnetic tape.
Storage systems may be located at multiple sites including multiple geographically distinct sites. The storage systems may communicate over one or more networks. Each storage system may include a plurality of clusters. Each cluster may include a plurality of tape drives. Magnetic tapes are mounted to the tape drives in order to read data from and write data to the magnetic tapes.
Each magnetic tape may be organized as one or more logical volumes, referred to herein as volumes. A volume may appear to a host as a distinct storage device. A volume may be logically “mounted” on a virtual tape drive. As used herein, a virtual tape drive is a logical construct that appears to a host as a tape drive.
Operations such as read operations and write operations for a virtual tape drive mounting a logical volume may be routed through a tape volume cache (TVC). The TVC may include a rapidly accessible storage device such as a hard disk drive. The storage device may cache data to the TVC. Thus the TVC may cache data that is read from the logical volume and/or cache data that is to be written to the logical volume. For example, a host may make repeated writes to a logical volume. The TVC may store the written data on a hard disk drive without writing the data to the logical volume's magnetic tape. At a later time, the TVC may write the cached data to the magnetic tape.
The storage systems may maintain multiple consistent copies of volumes. Two or more clusters with consistent copies may be able to provide access to the volumes. Unfortunately, a host has no way of determining which of the clusters should be used to most advantageously access a specified volume.